AURORA, Colo. -- James Holmes, the suspect in the Colorado shooting rampage, is described as a medical student from San Diego who dropped out of a doctoral program at the University of Colorado medical school last month.

A profile of the 24-year-old suspect is beginning to emerge only hours after a gunman opened fire in a crowded movie theater and killed at least 12 people.

USA TODAY's Kevin Johnson quotes federal law enforcement officials as confirming the identity of the shooting suspect as Holmes, but says he "was not on anybody's radar" and apparently did not have a record.

The Denver Post, citing "information provided" to the newspaper, reports that the suspect described himself last year in an apartment rental application as a student who was "quiet and easy going."

Denver's Fox31 reports that police documents show that he moved to Colorado from San Diego to pursue a PhD.

The Associated Press reports that Holmes began a program in neuroscience at the University of Colorado in the fall of 2011, but withdrew last month.

The suspect, who was dressed in black and apparently wearing a protective vest, was arrested by his car near the movie theater early today. He had an assault rifle, shotgun and two pistols at the scene, the Associated Press reports.

"He did not resist. He did not put up a fight," says Aurora police spokesman Frank Fania.

The suspect lives at an apartment about four miles from the theater where the shootings took place and in view of Children's Hospital, where some victims were taken.

The suspect told authorities there were explosives at his apartment, which was quickly surrounded by police, TheDenver Post reports.

Police said the apartment was booby-trapped with a "pretty sophisticated device" and evacuated about five apartment buildings in the are.

ABC News says it spoke to a woman in San Diego who identified herself as Holmes' mother. The woman immediately expressed concern that her son might be involved in the shootings in Colorado.

"You have the right person," she told ABC News. "I need to call the police... I need to fly out to Colorado."

KPBS reports that San Diego police have begun provided security for the woman, identified as Arlene Holmes, who lives in Rancho Penasquitos.